Power Factor Correction (PFC) circuits are widely used in power converters in order to correct the current phase and improve the power factor. FIG. 1 illustrates a waveform diagram in a PFC control. An input voltage Vin is a half-sine waveform signal, and is usually rectified from a commercial power which is an Alternating-Current (AC) sine wave. In order to implement PFC control, the waveform shape of an input current Iin needs to follow the waveform shape of its input voltage Vin, and the phase of input current Iin is the same with that of input voltage Vin. As shown, a relatively high input voltage Vin corresponds to a relatively low average input current Iin_avg. In a switching mode PFC circuit, the waveform shape of input current Iin has a saw tooth shape, and power factor can be improved by controlling the waveform shape of average input current Iin_avg of input current Iin to follow the waveform shape of input voltage Vout, and thus PFC control is fulfilled.
At the meantime, the international energy agency puts forward high requirements in power conversion efficiency of PFC circuit. However, light load efficiency of the present PFC products could not meet the requirements well.
Accordingly, an improved PFC circuit with high efficiency, especially the light load efficiency is required to at least address one or some of the above deficiencies.